Structural elucidation, distribution and antioxidant activity of bound phenolics from whole grain brown rice.

[Display omitted] • 4 new and 18 known compounds were isolated from brown rice bound phenolic extracts. • Three known phenolic compounds were reported from brown rice for the first time. • The contents of 22 compounds in brown rice, bran and polished rice were determined. • The ORAC, PSC, and CAA antioxidant activity of isolated compounds were measured. Chemical profiles, distribution, and antioxidant activity of bound phenolics from brown rice were investigated. Four new dehydrodiferulic acid dimers (DFA) along with eighteen known phenolics were isolated from brown rice bound phenolic extracts and their structures were determined by multiple spectroscopic methods. Among them, ferulic acid and 8–5′ DFA were the most abundant monomeric and dimeric bound phenolics in brown rice, rice bran and polished rice. In whole brown rice, polished rice contributed more than 50% of three phenolic monomers and six phenolic dimers, while rice bran contributed more than half of the other thirteen phenolics including eight monomers, four dimers, and one trimer. All the isolated compounds exhibited oxygen radical absorbance capacity. Thomasidioic acid, caffeic acid, methyl caffeate, and 8–5′ DC DFA displayed potent peroxyl radical scavenging capacity, and the last three compounds also showed moderate cellular antioxidant activity. [ABSTRACT FROM AUTHOR]